Irreversible Transformation
This subnode should be used to model thermally induced irreversible transformations in solids.
Irreversible transformation
Three models are available to define the material transformation. Select the Transformation model — Temperature threshold (the default), Arrhenius kinetics, or User defined. The first two models use integral forms over time to express the fraction of transformation θit as a function of temperature, while you can set it manually with the third option.
Temperature threshold
For Temperature threshold, select the type of analysis—Overheating analysis (the default) or Overcooling analysis, depending on the expected temperature variations. See the Parameters section for the additional settings specific to each type of analysis.
Arrhenius kinetics
For Arrhenius kinetics, define the parameters used in the Arrhenius equation to compute the degree of transformation (see Arrhenius Kinetics for more details):
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Frequency factor A in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
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Activation energy ΔE in the Arrhenius equation. Default is taken From material. For User defined enter a value or an expression.
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Polynomial order n of the (1-α) factor to define a polynomial Arrhenius kinetics equation.
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Enthalpy change L to define the enthalpy variation associated with the transformation. The following heat source is added to the right-hand side of Equation 6-12 in Solid node:
User defined
Enter values or expressions for the Enthalpy change L and the Fraction of transformation θit to define the heat source associated with the transformation as:
Specify Different Material Properties
Specific thermodynamics properties before and after complete transformation may be defined by selecting the Specify different material properties for the transformed state check box.
Choose a Transformed material, which can point to any material in the model. The default uses the Domain material. The properties before transformation are the ones specified in the Heat Conduction, Solid and Thermodynamics, Solid sections of the parent Solid node. The effective material properties are dynamically updated with the transformation evolution.
Parameters
Overheating Analysis
Enter values for:
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Transformation temperature Tit, h to define the (high) temperature that the solid needs to reach to start getting transformed.
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Transformation time tit, h to define the time needed for the complete transformation to happen while the temperature is above Tit, h.
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Enthalpy change Lit, h to define the enthalpy variation associated with transformation due to overheating. The following heat source is added to the right-hand side of Equation 6-12 in Solid node:
Overcooling Analysis
Enter values for:
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Transformation temperature Tit, c to define the (low) temperature that the solid needs to reach to start getting transformed.
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Transformation time tit, c to define the time needed for the complete transformation to happen while the temperature is below Tit, c.
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Enthalpy change Lit, c to define the enthalpy variation associated with transformation due to overcooling. The following heat source is added to the right-hand side of Equation 6-12 in Solid node:
Heat Conduction
This section is available when the Specify different material properties for the transformed state check box is selected.
Select a Thermal conductivity kd — From material (the default) or User defined, to be used for transformed solid. For User defined choose Isotropic, Diagonal, Symmetric, or Anisotropic based on the characteristics of the thermal conductivity and enter another value or expression in the field or matrix.
Thermodynamics
This section is available when the Specify different material properties for the transformed state check box is selected.
Select a Density ρd and Heat capacity at constant pressure Cp, d — From material (the default) or User defined, to be used for transformed solid. The heat capacity describes the amount of heat energy required to produce a unit temperature change in a unit mass.
For a detailed overview of the functionality available in each product, visit http://www.comsol.com/products/specifications/
Location in User Interface
Context menus
 Heat Transfer in Solids>Solid>Irreversible Transformation
More locations are available. For example:
Heat Transfer in Fluids>Solid>Irreversible Transformation
Ribbon
Physics Tab with Solid selected in the model tree:
Attributes>Irreversible Transformation